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Journal of Young Scientist, Volume II, 2014
ISSN 2344 - 1283; ISSN CD-ROM 2344 - 1291; ISSN Online 2344 - 1305; ISSN-L 2344 – 1283
RESTORING THE BUILDINGS USING THE 3D TEHNOLOGY
Dumitru-Lucian BLĂGESCU1, Ionuț-Alexandru BĂTRÎNACHE1
Scientific Coordinators: Bogdan ERGHELEGIU1, Mariana CĂLIN1
1
University of Agronomic Sciences and Veterinary Medicine of Bucharest, Faculty of Land
Reclamation and Environmental Engineering, 59 Mărăşti Blvd, District 1, 011464, Bucharest,
Romania
Corresponding author email: [email protected]
Abstract
There exists a very large amount of damaged buildings in Cultural Heritage in the old Centre of Bucharest. Common
damages are related with structural deformations (lack of verticality, crashes, e.g.) and the degradation of the support
(deteriorated materials, e.g.). Dense information is needed for both of them. Non-intrusive methods based in laser scans
provide a 3d support with dense information with a low human cost. Terrestrial laser scanners deliver a dense pointwise sampling of an object’s surface. In many respects, laser scanning follows the same general surveying process as
other instruments: data is collected in the field, adjusted to the appropriate coordinate system, and relevant features
can be extracted to produce deliverables ranging from topographic maps, coordinate values, 2D or 3D CAD drawings
etc.
Key words: 3D Laser Scanning, Cultural Heritage, damage building.
job”, combined with the selection of the most
appropriate hardware and software. According
to the laser scanning users’ community, the
survey planning should at least contain the
following topics:
-Determining the goals and objectives;
-Analysing the area to be surveyed;
-Determining the measuring techniques and
equipment;
-Data management.
Surveying with a 3D laser scanner generates a
new set of information – the point cloud. A
point cloud can be compared with
photogrammetry in that it is derived from a
remote sensing instrument, that is, the
measurements are taken without physically
contacting the target area. Lastly, a comparison
can also be made to remote sensing satellites,
as additional “non-positional” data is collected
from the raw measurements, such as the signal
intensity of each point in the cloud, which will
vary based on the reflectivity of the scanned
object. Each point in the point cloud is
measured with respect to the scanner position,
and similar to photogrammetry, the position of
the scanner (the camera) does not need to be
known during the measurements. Aligning the
point cloud to local control with laser scanning
INTRODUCTION
Years ago, the measurement of any object was
exclusively done with theodolites or total
stations. With the increasing usage of 3D CAD
design tools the need for better, more accurate
and faster 3D measurement grew in parallel.
3D Laser Scanning describes a method where a
surface is sampled or scanned using laser
technology. The word LASER is an acronym
for Light Amplification by Stimulated
Emission of Radiation. The first working laser
was demonstrated in May 1960 by Theodore
Maiman at Hughes Research Laboratories [7].
The data collected through laser scanning can
be used to construct digital, two-dimensional
drawings or three-dimensional models useful
for a wide variety of applications. In the early
stages, laser scanning was short range and
mainly used in the automotive and industrial
design process to facilitate the Computer Aided
Design (CAD) process. Mid-range scanners
were developed for the petrochemical industry.
Due to the complexity of plants, which were
only documented as 2D drawings. However the
key to success in using 3D laser scanning
remains the setup and implementation of the
right methodology and workflow “fit for the
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scanner and control the properties of the
scanner through LeicaHDS Cyclone software.
This software provides the tools to
automatically detect artificial targets in the scan
(Figure1). Powerful yet affordable 3D point
cloud visualisation (Figure2), measurement,
mark up, and data exchange software for
professionals.
Leica Cyclone BASIC provides professionals
with a set of tools for efficiently managing and
executing laser scanning/High Definition
Surveying (HDS) projects.
Professionals can collect and analyse laser scan
data, while collaborating for better informed
project decisions. In the field, Cyclone BASIC
operates time-of-flight and phase-based Leica
Geosystems scanners. Users can manage scan
parameters; scan target acquisition; field QA;
digital imaging; geo-referencing; and more
depending on scanner capabilities.
In the office, Cyclone BASIC provides viewing
and navigating of point clouds and 3D models,
as well as measurement and mark-up/redlining.
Cyclone BASIC is a versatile “back-office
„data-exchange module, supporting imports
and exports of a wide range of formats.[5]
is similar to photogrammetric control, as
overlapping targets can be used to join multiple
scans (photos) together and to “fit” it to the
desired coordinate system. The survey
preparation phase includes the decision making
on the registration technique to be used. These
techniques can be subdivided into three
categories: registration using 3D re-sectioning
of scanned targets, registration by setting the
laser scanner over known control points, and
registering using cloud to cloud constraints [8]
The recording of position, dimensions and/or
shape is a necessary part of almost every
project related to the conservation of cultural
heritage, forming an important element of the
documentation and analysis process. For
example, knowing the size and shape of a
topographic feature located in a historic
landscape can help archaeologists identify its
significance; knowing how quickly a stone
carving is eroding helps a conservator to
determine the appropriate action for its
protection; while simply having access to a
clear and accurate record of a building façade
helps a project manager to schedule the work
for its.[1]
MATERIALS AND METHODS
At present there is no standard procedure for
survey planning for terrestrial laser scanning.
To collect data used in our example we used a
LeicaScanStation2.
Figure 2. A damage balcony on a building located on
French Street, Bucharest (seen on Cyclone software)
Figure 1. Reflective target setup over common points
used to link neighboring scans
Before starting the scanning, the scanning
device itself was connected to a laptop that can
receive and store all the points coming from the
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Figure 4. Points cloud representing the façade of the
building located in Old Centre, Bucharest
Laser scanning might have a use at any stage of
a project. Tasks that might be considered as
potentially suitable for the application of laser
scanning could include any of the following:
• contributing to a record before renovation of a
subject or site, which would help in the design
process as well as contribute to the archive
record;
•
contributing to a detailed record where a
feature, structure or site might be lost or
changed forever, such as in an archaeological
excavation or for at a site at risk; (Figure 5)
Figure 3. Leica Scan Station 2
The Leica Scan Station (Figure 3) 2 is a pulsed
type, laser Class 3R, laser scanning system that
has a modelled surface precision (noise) of 2
mm, an scan resolution of 6 mm (Gaussian based) for position and 4 mm (FWHH - based)
for distance at a range of 0m-50 m, the
maximum range being 300 m at 90% (134 m at
18%) and a maximum instantaneous scan rate
up to 50.000 points/sec. The maximum fieldof-view (per scan)of the scanner is 360°
horizontal and 270° vertical and has an optical
sighting using the Quick Scan™ button.
Laser scanning from any platform generates a
point cloud (Figure 4): a collection of XYZ coordinates in a common co-ordinate system that
portrays to the viewer an understanding of the
spatial distribution of a subject. For most laser
scanning instruments, the point cloud can be
regarded as the ‘raw product’ of a survey. The
point cloud may also include additional
information, such as return intensity or even
colour values. Generally, a point cloud contains
a relatively large number of co-ordinates in
comparison with the volume the cloud
occupies, rather than a few widely distributed
points.[9]
Figure 5. Laser scanning for historic sites at risk, St
Mary’s Church Whitby, North Yorkshire.
•
structural or condition monitoring, such
as looking at how the surface of an object
changes over time in response to weather,
pollution or vandalism;
•
providing a digital geometric model of
an object from which a replica can be generated
for display, or as a replacement in a restoration
scheme; (Figure 6)
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RESULTS AND DISCUSSIONS
It is unlikely that professionals in the heritage
sector who require laser scanning data or
products will themselves have the means or
expertise to undertake the work. It is more
likely that survey work will need to be
commissioned and undertaken by a specialist
contractor. The following tips will help when
preparing to commission a survey.
•
Consider the level of detail required and
the extent of the subject. These are often the
overriding parameters used to determine the
appropriate survey technique and/or deliverable
product.
•
Start by working out what data are
needed in order to answer the questions you
have set. Try to come up with requirements for
accuracy and products. It may not be necessary
to specify the actual technique to be used, just
the required products.
•
Before you commission and procure the
data, consider how you will use the product;
additional costs might be hidden in buying new
software/hardware.
•
Discuss the requirements with possible
contractors. A good contractor will be able to
advise you if your requirements are achievable,
realistic and necessary, as well as provide
information on an alternative deliverable
product that you may not have considered. Also
discuss the work with other members of your
organisation, especially with those with
relevant expertise, as other uses for the survey
data and products may be apparent to them, and
may increase the overall value of the work to
be commissioned.
•
Consider how the collected survey will
be archived and made available for use in the
future. Take advice from national organisations
such
as
the
National
Cultural
Heritage.Determine who will own the collected
data and the delivered product.
•
Finally, prepare a project brief, using a
standard document as a base, such as that
published by English Heritage (eg Andrews, et
al 2009 Metric Survey Specifications for
Cultural Heritage). [2]
Figure 6. An original and replica bust of the Emperor
Caligula generated from data collected by air
triangulation laser scanner (courtesy of Conservation
Technologies, National Museums Liverpool)
•
contributing
to
three-dimensional
models, animations and illustrations for
presentation in visitor centres, museums,
through the internet and through the media
(enhancing accessibility/ engagement and
helping to improve understanding);
•
aiding
the
interpretation
of
archaeological features and their relationship
across a landscape, this contributing to
understanding about the development of a site
and its significat change to the area;
•
working, at a variety of scales, to
uncover previously unnoticed archaeologically
significant features – such as tool marks on an
artefact – or looking at a landscape covered in
vegetation or woodland
• spatial analysis, not possible without threedimensional data, such as line of sight or
exaggeration of elevation. [3]
It is important to recognise, however, that
laser scanning is unlikely to be used in
isolation to perform these tasks. It is highly
recommended that photography should also
be collected to provide a narrative record of
the subject. In addition, on-site drawings,
existing mapping and other survey
measurements might also be required to aid
interpretation and understanding.
Asking the following questions will help you to
better understand what your requirements are
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and whether laser scanning, in its various
forms, is suitable. It will also help to identify
possible alternatives.
What outputs are wanted?
Scanning can contribute to a whole range of
outputs, so deciding what outputs you require
will help to determine an appropriate project
brief. Outputs might include a highly edited
surface mesh, two-dimensional drawings,
rendered movies or even virtual environments.
Other forms of data, such as images and survey
control, are likely to be required to contribute
to these outputs.
The scale of your output is a key decision,
which will help determine the accuracy of the
product and the required point density.[4]
What level of accuracy is required?
This is typically related to object size and the
purpose of the survey. A common answer is
‘the best that you can do’, but this is not always
helpful in deciding what type of technique
should be used. It is perhaps more correct to
ask what is the optimum accuracy that balances
the needs of the task, the capability of the
technique and the budget available
Figure 7. Laser scanning from an extra tall tripod
Is three-dimensional information required?
If yes, consider how the information is going to
be used. This will help you or the contractor to
determine the processing that will be required
on the laser scanning data. Even if the answer
is no, and you only need two-dimensional
measurements and dimensions, laser scanning
may still be useful. Laser scanning can be used
to provide line drawings in elevation, section,
and plan. It is especially useful when access to
a site makes it difficult to use conventional
methods. The way in which laser scanning
enables direct integration of the collected data
on site can also help a contractor to reduce the
likelihood of revisits.[6]
Time and access restrictions?
Access and time might be unlimited. For
example, the object might be brought to a
studio-based scanner. Alternatively, access to
the subject may be easy, perhaps because
temporary scaffolding is in place, but time may
be restricted because the scaffolding will be
dismantled, making future access impossible
unless new scaffolding is erected. Note that
while scanning from a static position requires a
stable platform (Figure 7), scanning from
scaffolding or from a mast or hydraulic
platform is possible, although care should be
taken to ensure that the scanner remains stable
during operation .
Access might be restricted on health and safety
grounds, because a building is unsafe, making a
survey possible only from a few locations. In
an archaeological excavation, survey may be
time-critical, as recording is required at each
part of the excavation and cannot be repeated.
This requires scanning to be available on site
during excavation.
Budget
Although laser scanning is still generally
regarded as a high-cost technique, it can be
justified, as the information required may not
be available in any other way. If the budget is
limited, or non-existent, laser scanning
probably is not a technique that you can use.
Where it is adopted, it is advisable to try to
ensure that it can be used in many different
ways, so as to provide best value from its
commissioning. A number of measured
building survey contractors have found that
laser scanning is a cost-effective route to
159
combination with the DLR Panoramic Colour
Camera a precise and accurate monitoring of
the actual environment
by means of colour point clouds is
achieved. This is unique due to its high
precision and quality.
producing plans and elevations due to the
reduced time on site as compared with
conventional survey methods. For a large
organisation the savings could fairly quickly
compensate for the high initial capital outlay.
Can you do this yourself?
It may be possible to undertake the data
collection and data processing yourself.
However, scanning requires specialist skills in
order to achieve a precise and reliable product.
This might include techniques for providing
precise survey control measurement and/or
knowledge of 3D CAD or GIS software. If this
is your first project, using a contractor is
advisable.
REFERENCES
3D Laser Scanning for Heritage (second edition)
Andrews, D et al 2010 Measured and Drawn:
Techniques and Practice for the Metric Survey of
Historic Buildings (2 edn). Swindon: English
Heritage
CIPA2001: Surveying and Documentation of
Historical Buildings-Monuments-Sites. Traditional
and Modern Methods, CIPA Intl workshop
(Potsdam, Germany), 2001.
Crutchley, S and Crow, P 2009 The Light Fantastic:
Using Airborne Lidar in Archaeological Survey.
Swindon: English Heritage
Cyra Technologies, Inc.: “Cyclone 4.0-User’s manual”
Dallas, R W A 2003 A Guide for Practitioners:
Measured Survey and Building Recording.
Edinburgh: Historic Scotland
Fröhlich, C.; Langer , D.: “3-D Ladar for Heinz, I.;
Mettenleiter, M.; Haertl, F.;
http://hds.leica-geosystems.com/en/
Inspection of Real World Environments“. 5th ISPRS
Conf. on Optical 3-D Measurement Manual”.
CONCLUSIONS
With the developed visual laser scanner, the
control software and the software for model
generation,very powerful tools are available
that are suitable for most cultural heritage
surveying tasks. The developed laser scanner
offers high accuracy measurements in
conjunction with a high sampling rate and large
dynamic range inreflective properties of object
surfaces (highly reflective to absorbing). In
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